The objectives of the project are: To assess whether cAMP- dependent protein kinases are enzymic links necessary for the biological action of cAMP when the inhibition of tumor growth is induced in vivo; to investigate whether DBcAMP-responsiveness (tumor-regression with dibutyryl cAMP injection to host animal) can be correlated with physicochemical properties of catalytic or regulatory subunits of protein kinase; to test whether cAMP-stimulated phosphorylation of cellular proteins is correlated with DBcAMP-responsiveness.